The MRI apparatus is an apparatus that measures an NMR signal generated by an object, especially, the spins of nuclei that form human tissue, and images the shapes or functions of the head, abdomen, limbs, and the like in a two-dimensional manner or in a three-dimensional manner. In the imaging, according to a sequence set in advance, NMR signals having been subjected to different phase encoding and frequency encoding by the gradient magnetic field are measured as time series data. Then, the measured NMR signals are reconstructed as an image by a two-dimensional or three-dimensional Fourier transform.
In the non-orthogonal sampling method, such as a radial sampling method or a hybrid radial method, data required for reconstructing one image is obtained by performing sampling by radially scanning the measurement space at various rotation angles with approximately one point (generally, the origin) of the measurement space as the rotation center. It is known that radial sampling is resistant to artifacts due to body motion. However, scanning trajectories (blades) overlap each other in the measurement space. For this reason, if the positional relationship between the blades is not appropriate or the phase difference at the intersection between the blades occurs, the image quality of the reconstructed image is degraded.
Hereinafter, in this specification, one straight trajectory in the radial sampling method and a plurality of parallel straight trajectories in the hybrid radial method will be referred to collectively as a blade.
However, in the actual imaging, due to non-uniformity of the static magnetic field or the output error of the gradient magnetic field, the arrangement position of each blade in the measurement space is different from the calculated arrangement position (coordinates) or a phase difference occurs at the intersection between the blades. As a technique for correcting the error of the arrangement position of the blade, there is a method of acquiring data for calculating the shift amount of the blade position caused by the output error of the gradient magnetic field, calculating the shift amount of each blade on the k-space, and correcting the error of the arrangement position of each blade during the image reconstruction processing (for example, refer to PTL 1).